Figure 211

Algorithm for differentiating among the major categories of small vessel vasculitis that affect the kidneys. In a patient with signs and symptoms of small vessel vasculitis, the type of glomerulonephritis is useful for categorization. Identification of IgA nephropathy is indicative of Henoch-Schonlein purpura. Type I membranoproliferative glomerulonephritis (MPGN) suggests cryoglobulinemia and/or hepatitis C infection, and pauci-immune necrotizing and crescentic glomerulonephritis suggest some form of ANCA-associated vasculitis [1,2]. The different forms of ANCA vasculitis are distinguished by the presence or absence of certain features in addition to the necrotizing vasculitis, ie, granulomatous inflammation in Wegener's granulomatosis, asthma and blood eosinophilia in Churg-Strauss syndrome, and neither granulomatous inflammation nor asthma in microscopic polyangiitis. Approximately 80% of patients with active untreated Wegener's granulomatosis or microscopic polyangiitis have ANCA, but it is important to realize that a small proportion of patients with typical clinical and pathologic features of these diseases do not have detectable ANCA.

Vasculitis (Polyarteritis Nodosa, Microscopic Polyangiitis, Wegener's Granulomatosis, Henoch-Schonlein Purpura) APPROXIMATE FREQUENCY OF ORGAN SYSTEM INVOLVEMENT IN SMALL VESSEL VASCULITIS

Henoch-Schonlein Cryoglobulinemic Microscopic Wegener's Churg-Strauss

Organ system purpura, % vasculitis, % polyangiitis, % granulomatosis, % syndrome, %

Renal 50 55 90 80 45

Cutaneous 90 90 40 40 60

Pulmonary <5 <5 50 90 70

Gastrointestinal 60 30 50 50 50

Musculoskeletal 75 70 60 60 50

Neurologic 10 40 30 50 70

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